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Radiochromic Film Measurement of Nanoparticle Radiation Dose Enhancement

M Buczek

M Buczek1*, G Lawes2, M Snyder1, Y Hillman1, J Rakowski1, (1) Wayne State University School of Medicine, Dept. of Radiation Oncology, Detroit, MI,(2) Wayne State University Dept. of Physics, Detroit, MI,

SU-E-T-103 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Bombardment of high-Z material with x-ray radiation leads to release of fluorescent x-rays, photoelectrons, and Auger electrons. The electrons deposit their energy in tissue within micrometers distance of the high-Z material surface when in contact with tissue. Gold nanoparticles have been studied as a high-Z vehicle for taking advantage of that phenomenon to enhance radiotherapy dose at the cellular level. Our goal is to use unlaminated radiochromic film to measure the gold nanoparticle dose enhancement factor (DEF) associated with 40 and 50 kVp tungsten bremsstrahlung spectrums.

Methods: A 10 nm gold foil was placed between an x-ray source and radiochromic film and exposed to lightly filtered 40 kVp and 50 kVp tungsten bremsstrahlung x-rays. A Monte Carlo simulation was performed to estimate the energy deposition with depth in the film active layer, and energy deposition with depth in water. The film was calibrated at x-ray energies ranging from 4.5 keV to 50 kVp to account for energy-dependent response. Optical densities of film exposed with and without gold nanoparticles were used to derive a dose enhancement factor, defined as the ratio of dose attributed to Auger electrons to dose attributed to bremsstrahlung x-rays.

Results: Dose enhancement factors within the mean pathlength of Auger electrons ranged from 34.6 +/- 8.6 to 45.0 +/- 11.0 for the 40 kVp spectrum, and 30.7 +/- 11.0 to 44.2 +/- 7.7 for the 50 kVp spectrum.

Conclusion: These results compare favorably with other studies that have found varying gold nanoparticle DEF values for 50 kVp bremsstrahlung by Monte Carlo calculation ranging from 1.5 to 2 within a tumor volume to 400 within 10 μm of the gold nanoparticle/tissue interface. Measurements by thermally stimulated exoelectron emission beryllium oxide dosimetry⁺ found a DEF of 55.7 in a single layer of cells on thick gold foil.

Funding Support, Disclosures, and Conflict of Interest: Wayne State University Fund for Medical Research and Education

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